In many electronic apparatuses, cooling is a vital issue to ensure them operating in a desired temperature for better performance. Chips are always the main heat sources of electronic apparatuses. Therefore, many cooling devices are designed to cool the electronic apparatuses, especially in chips. Traditionally, the cooling devices, such as fin, foaming material, fan, and heat pipe, improves the thermal conductivity of heat source by increasing thermal-conductive area, circulating thermal-convective fluid, and employing cooling media. However these cooling devices are not efficient enough to cool the modern electronic apparatuses with chips of high circuit integration generating huge thermal energy.
A miniature pumping system, which is fabricated on a substrate by micro electro mechanical (MSMS) technology, is a new approach to solve the cooling issue of chips. The miniature pumping system employs mini pump to convey working fluid circling around a heat source, such as a chip, for cooling it. Because the mini pump's size is on the order of several millimeters, the fabrication of miniature pumping system still faces challenges and needs more studies.
Another novel cooling device is a micro-miniature stirling cycle cooling engine, which implants a stirling cycle cooling engine in a silicon based matrix by semiconductor processing technology. The Stirling Cycle describes the behavior of ideal gas during a period of expansion and compression. According to the stirling cycle, the ideal gas absorbs heat during expansion and ejects heat during compression. A conventional stirling cycle cooling engine employs a vessel in which the volume of fluid could be expanded and compressed, so that heat can be absorbed from a heat source during expansion and ejected out of the vessel during compression. The higher frequency of the stirling cycle increases the cooling efficiency the stirling cycle cooling engine. In U.S. Pat. No. 5,590,534, it is reported that the general frequency of conventional stirling cycle cooling engine is about 50 Hz. In U.S. Pat. No. 5,457,956, it is disclosed a micro-miniature stirling cycle cooling engine implanted in a silicon-based matrix. Because of the further reduced size, the microminiature stirling cycle cooling engine can be operated in a frequency higher than 500 Hz, thereby providing a better cooling efficiency. In addition, the micro-miniature stirling cycle cooling engine can be directly fabricated on the back side of chip so as to tightly bond between the cooling engine with the chip.
Even though the micro-miniature stirling cycle cooling engine has remarkably improved the conventional stirling cycle cooling engine, it still exists several needs and disadvantages. The smaller size of the micro-miniature stirling cycle cooling engine has, the higher cooling efficiency it has, due to the fluid therein acting more like the ideal gas. Therefore, there is a need to further downsize the cooling engine. In addition, sicne the thermal distribution of heat source is not uniform over its surface and the single micro-miniature stiling cycle cooling engine doesn't pump heat evening, there's also a huge need to optimize cooling capacity distribution of micro-miniature stirling cycle cooling engine. Additionally, the micro-miniature stirling cycle cooling engine of U.S. Pat. No. 5,457,956 employs a piezoelectric layer as an actuator to drive a diaphragm for expanding or compressing the fluid. However, the piezoelectric layer costs a period time to deformation due to its hysteresis. Furthermore, fabricating the micro-miniature stirling cycle cooling engine on the back side of chip would raise a risk to damage the chip by added process, such as further thermal treatment. For forming a cooling engine, the cost of chip is too high to be wasted in a failed fabrication.
Accordingly, there is a huge need to improve the micro-miniature stirling cycle cooling engine for adapting to modern electronic apparatuses and chips.